Two blocks of masses 20 kg and 8.0 kg are connected together by a light string and rest on a frictionless level surface. Attached to the 8 kg mass is a second light string, which a person uses to pull both blocks horizontally. If the two-block system accelerates at 0.5 m/s2, what is the tension in the second string attached to the 8 kg mass?
a) 14 N
b) 6.0 N
c) 10 N
d) 4.0 N